In a battery operated power supply, a D.C.--D.C. converter is, generally, employed in order to regulate a voltage from a battery. High D.C. voltage is obtained from the battery through the use of a voltage converter. A converter includes a transformer for converting low D.C. voltage to high A.C. voltage, and a rectifier circuit for rectifying the A.C. voltage, the rectified voltage being then applied to a storage capacitor in order to charge it. The power supply of this kind of the load employs a D.C.--D.C. converter which comprises a direct current power source circuit having a battery, a voltage converter circuit for converting a direct current output voltage to an alternating current voltage, a rectifier circuit for rectifying the alternating current voltage into a direct current voltage.
These power supply are, typically, employed in electric flash units. Since an electric flash unit of this type is generally portable, the transformer of the converter circuit is needed to be made small in order to make a power supplying apparatus small and light.
FIG. 1 shows an example of a prior art power supplying apparatus. The apparatus shown in FIG. 1 comprises a direct current power source circuit including a battery 2 and a power source switch 1 which is connected to the battery 2 in series relationship, a voltage converter circuit comprising an oscillator circuit having an oscillating resistor 3, an oscillating transformer 4, an oscillating switch element in the form of a transistor 5 and an oscillating capacitor 6, a rectifier circuit which includes a diode 7 of which a cathode electrode is connected to one terminal of a secondary winding 4b of the oscillating transformer and a capacitor 8, and an electric charge storing circuit which includes a main storage capacitor 9. In the voltage converter circuit, the oscillating transformer 4 has a primary winding 4a, the secondary winding 4b and a third winding 4c. One terminal of the primary winding 4a is connected to a positive terminal of the battery 2. The other terminal of the primary winding 4a is connected to a collector electrode of the transistor 5. An emitter electrode of the transistor 5 is connected to a negative terminal by way of the power source switch 1. The other terminal of the secondary winding 4b is connected to a base electrode of the transistor 5. The third winding 4c of the oscillating transformer 4 is connected between the positive terminal of the battery 2 and the base electrode of the transistor 5 by way of the oscillating resistor 3. The oscillating capacitor 6 is connected between the base electrode and the emitter electrode of the transistor 5.
In the power supplying apparatus of FIG. 1, when the power source switch 1 is closed, the voltage converter circuit activates an oscillating operation, and thereby the high voltage is induced at the secondary winding 4b of the transformer 4. The boosted alternating current voltage is rectified by the diode 7 of the rectifier circuit, and thereafter electric charge is stored on the main storage capacitor 9 of the electric charge storing circuit. When the electric charge stored on the capacitor 9 reaches a predetermined value, a predetermined voltage appears between output terminals 10a and 10b.
In this known power supplying apparatus, the oscillating transformer 4 is provided with three windings, that is, the primary winding 4a, the secondary winding 4b and further the third winding 4c. Accordingly, the voltage converter circuit of the power supplying apparatus is complicated, and thereby the apparatus becomes complicated and bulky, as well as is expensive.